In the winding of strand material onto reels, the material is typically wound onto the reel in layers with each layer containing successive convolutions of the strand material distributed uniformly between front and back flanges of the reel. To prevent undesirable build-up of the strand material at spaced locations on the reel, it is important to control the length-of-travel of a reciprocating strand distributor between the reel flanges.
In one method of controlling the reciprocating strand distributor, a reversible stepper motor drives the distributor between a pair of limit switches which facilitate reversal of the direction of travel of the motor. In this method, the pair of limit switches are spaced to represent the respective ends of the reel. The reciprocating distributor moves adjacent to the reel and distributes the strand material onto the reel until the distributor engages and operates the limit switch at one end of the reel. The stepper motor is then controlled to reverse the direction of travel of the distributor. The distributor travels in the reverse direction while distributing the strand material onto the reel until the distributor engages and operates the limit switches at the other end of the reel. The stepper motor is again controlled to reverse the direction of distributor travel. This pattern of operation continues to provide the reciprocating movement of the distributor. A distributor system employing limit switches is disclosed in U.S. Pat. No. 3,829,037.
Limit switches must be constantly adjusted and checked for malfunction. If the switch becomes defective or if the reciprocating distributor does not properly engage and operate the switch, the distributor may stall in one position near one flange of the reel and cause an undesirable build-up of strand material at this one position.
Another known method of controlling the reciprocating distributor utilizes digital techniques. This system includes a stepper motor to drive the reciprocating distributor adjacent to the reel. Thumbwheel switches are used to establish a count representing the ends of the reel. A rotating pulse generator is fixedly attached to the shaft of the stepper motor to develop a signal representing the distance traveled by the distributor. As the stepper motor rotates, the output of the rotating pulse generator is stored as a count to theoretically represent the instantaneous location of the distributor. Digital circuits are used to compare the stored count with the count established by the settings on the thumbwheel switches. When a coincidence occurs between the stored count and the count of one of the thumbwheel switches, a signal is developed which represents an end-of-travel point of the reciprocating distributor. The stored count increases or decreases depending on whether the reversal of the stepper motor occurred at the front or back flange of the reel. The distributor continues to reciprocate until a full reel of strand material has been attained.
This system is a discrete system. Therefore, if an extraneous pulse occurs, the pulse causes the stored count to indicate an erroneous instantaneous location of the distributor. As a result of the erroneous stored count, the reciprocating distributor is prevented from uniformly distributing strand material between the front and back flange which may cause a build-up of strand material on the reel.
Another method of controlling the reciprocating mechanism using digital techniques is illustrated in U.S. Pat. No. 3,876,166. This method facilitates the winding of the strand material onto bobbins in a package such that the ends of the strand-material package are of a trapezoidal shape. The technique illustrated therein uses a system for producing stroke pulses each time the reciprocating distributor travels a predetermined distance. The number of stroke pulses are counted as the reciprocating mechanism passes a central reference position. The reciprocating distributor is reversed when the number of pulses counted coincides with a setpoint value representing one of two end-of-travel points. The end-of-travel points are automatically sequentially reduced about the central reference position so that the stroke of the reciprocating distributor is gradually reduced to produce the trapezoidal shape at the ends of the strand-material package.
Consequently, there exists a need for a system to accurately control the movement of a reciprocating mechanism to provide for uniform distribution of strand-material being wound onto a reel.